Electromagnetic stirrer



Aug. 6, 1968 G. KARLSSON ET AL 3,396,228

ELECTROMAGNETIC STIRHER 2 Sheet us 1 Filed 2, 1965 E M w N06 mu *T E m: T A! A o F A in "0A GK W. B

ELECTROMAGNET I C ST I RRER Filed Aug. 2, 1965 2 Sheets-Sheet 2 GsTA KARLSON KARE FOLGERO United States Patent 3,396,228 ELECTROMAGNETIC STIRRER Giista Karlsson and Kare Folgerii, Vasteras, Sweden, as-

signors to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, 2 corporationof Sweden Filed Aug. 2, 1965, Ser. No. 476,578 4 Claims. (CI. 13-46) ABSTRACT OF THE DISCLOSURE An electromagnetic stirrer for metallurgical furnaces polyphase coils, the different windings of which are arranged on a laminated core, has a mass with the permeability of about the permeability of air enclosing the outer ends of said windings. Said mass comprises filling material and a binding agent, the filling material being sand or ceramic material and the binding agent being a plastic material, the filling and binding agents being mixed together. A cover of a ceramic material covers the stirrer coils and adjacent parts.

The following invention relates to an electromagnetic stirrer for metallurgical furnaces, in which the windings of polyphase coils are arranged on a laminated core.

In furnaces for melting and/or heat retaining of iron or its alloys, for example are furnaces or metallurgical vacuum treatment furnaces, below the furnace bottom and outside the outer side wall of the furnace a polyphase winding is often arranged, fed with low frequency current, which winding is arranged around an iron core or an iron yoke. The winding with its iron yoke is placed under the furnace bottom, the latter being made of nonmagnetic metal, whereby stirring in the melt is obtained when current is fed into the winding. Such an electromagnetic stirrer is shown in the U.S. Patent 2,513,082.

The stirrer winding itself is usually wound flat and the different current conductors, usually several per coil, are often made with internal fluid cooling. The coils are placed in grooves in a laminated iron core and the ends of the windings outside this core are bent into a direction almost or exactly parallel with the lamination planes. It is a problem to protect these ends of the windings and adjacent portions of the windings and spacers between the windings against mechanical and thermal influences, against fouling with accompanying drawbacks, such as insulation faults, etc. and different steps have been taken to prevent such consequences. For example, the use of bolts or the like at the ends of the windings for fastening different protective layers has been tried which has, however, increased the price of the stirrer and which has not always been enough to eliminate the risks of damage to these ends. Simultaneously it has been desired to make the ends of the windings and their protective means in such a manner that a compact stirrer construction is obtained, which has also been a problem.

The invention relates to a solution of these and other corresponding problems and is characterised in that the ends of the windings are cast in a mass with a permeability of not more than about the same as the permeability of the air, the mass consisting partly of a filling material, such as a mineral and/or a ceramic material, and partly of a binding agent. Such a device is simple to manufacture. Ready-manufactured stirrer windings with inserted spacers and coupled cooling medium conduits etc. are cast into the mass at the ends of the windings. This means a simple and effective protection for the ends of the windings, and also there is obtained a satisfactory insulation for these ends and adjacent portions of the conductors and also a good fastening for the cover for the coils, known of itself, manufactured in ceramic ma- 3,396,228 Patented Aug. 6, 1968 terial and serving as a protection against melt overflowing against the stirrer.

In a preferred embodiment the mineral consists of coarse or fine sand, and the binding agent of a plastic material, such as at least one polyester, The binding agent may also be cement or an asphalt product. A construction with coarse or fine sand and plastic material (polyester) becomes mechanically especially strong, but also a construction with concrete has a satisfactory strength.

The invention is exemplified in the following figures, FIG. 1 of which schematically shows a stirrer below a furnace bottom, FIG. 2 a stirrer with partly cast-in ends of the windings, shown along the section A--A in FIG. 3, which in turn shows a longitudinal section of a stirrer, FIG. 4 is a top plan view of the lower right corner of the stirrer. FIG. 5 is a cross-section of the line 5-5 of FIG. 4. Under the non-magnetic bottom 11 (FIG. 1) of a metallurgical furnace 12 is arranged an electromagnetic stirrer 13, in the ease shown with straight legs. A more detailed part of this stirrer is shown in FIG. 3. A cover 20 of ceramic material separates the stirrer from the air gap at the furnace bottom. The coils 15 of the polyphase winding are laid in grooves 17 in a laminated iron core 16 (FIG. 2) and the ends of the windings 18 are bent into a direction close to or exactly parallel with the lamination planes of the iron core 16. To the right in FIG. 2 are shown ready-wound coils with ends of the windings before the casting. At the ends of the iron core there are placed inner frames 19 of steel sheet or similar material. Possibly spacers of insulating material may be placed between the ends of the windings 18, after which the ends are cast in a mass with a permeability of about the permeability of air. a should be 21 or 51, but, however, close to 1. (The permeability of air=1,000,000',365.) The mass may consist of coarse or fine sand mixed with a plastic material, such as polyester. The mass may also consist of concrete, light concrete and/or of a ceramic material, mixed with cement or a plastic binding agent or an asphalt product. In certain cases it may be preferable first to cast in or otherwise insulate the ends of the windings in, for example, a polyester, after which around these insulated ends there is cast a mass of the kind described above. By means of the casting method it may be possible to avoid separate spacers as the mass acts as spacers between the ends of the windings. In order to obtain satisfactory mechanical strength the smallest thickness of the mass outside the utmost end of the windings is to be at least the thickness of the winding end. In inward direction the cast body is defined by the sheets 19, and the outer face is completely or partly defined by the casting mould, which normally is removed after completion of casting in the direction perpendicular to the air gap the cast body 14 should extend a distance at least corresponding to the total vertical distance between the bent ends of the windings 18 and the upper plane of the same windings, whereby between this cast body 14 and the plastic casting around the ends 18 there will be provided a space for cooling means for cooling the ends of the windings 18 (coil ends) (not shown).

At the air gap there is placed a ceramic cover 20, as a protection for the stirrer windings 15, for outflowing melt and for undesired heating of the stirrer. By means of the slight V-form of the stirrer body at the air-gap a gutter 21 is defined for any escaping melt. The ceramic cover 20, which may easily be fastened to the cast body, for example in connection with the casting, is also formed to enclose protruding groove teeth 22, etc. of magnetic material (see 14, FIG. 3) close to the air gap, which teeth together with the coils 15 and other parts are clamped against the iron core by means of insulated bolts 24 extending through the same. Through a special construction of the upper end of the cast body the fastening of the cover'may be facilitated. The lowest part of the stirrer 21 is also the transverse axis 21 in FIGURE 4, along which the two planesof the stirrer cross.

The different longitudinal parts 15 of the winding are held between teeth of magnetic material 22. Said teeth of magnetic material which fill the space between the adjacent parts of the windings 15 are interrupted at their upper portions by clamping means, fastened by insulated bolts 24, said clamping means comprising fittings 23 and extending perpendicularly to the longitudinal direction of the windings 15 (FIG. 4). The ends of the windings 18 are bent down as shown in FIGURE 2 and are 'cast in a mall 14 with a permeability of about the permeability of air, for example a mass coarse or fine sand and a binding agent (polyester or cement). The teeth of magnetic material 22 extending opposite the air gap of the stirrer are placed in grooves or spaces between the adjacent parts of the windings. The mass 14 (FIGURE 2) completely encloses the ends of the windings 18 and a portion extends outside the outer parts of the ends 18.

The stirrer, which in ready manufactured condition for example has the structure shown in FIG. 3 and FIG. 2, left part, is resistant to careless treatment, for example during transport and erection and naturally also in mounted condition. An advantage of the stirrer is that only the ends of the stirrer are embedded in a cast mass, but that the active parts of the stirrer windings and the iron core are not embedded, and the weight may be kept down and at the same time a protection for the most sensitive parts of the mechanical structure is obtained,

The invention and its ranges of application may be varied in different ways within the scope of the following claims.

We claim:

1. Electromagnetic stirrer for metallurgical furnaces comprising polyphase coils, the different windings of which are arranged on a laminated core, and a mass with a permeability of about the permeability of air, enclosing the outer ends of said windings, said mass comprising comprising ceramic material and the binding agent being v a plastic material, said filling and binding material being mixed together.

3. Electromagnetic stirrer in accordance with claim 1, the outer ends of the windings being covered with plastic material around which is applied said compound of filling material and binding agent.

4. Electromagnetic stirrer for metallurgical furnaces comprising polyphase coils, the different windings of which are arranged on a laminated core, and a mass with a permeability of about the permeability of air, enclosing the outer ends of said windings, said mass comprising filling material and binding agent, said filling material consisting essentially of coarse or fine sand and the binding agent being a plastic material, said filling and binding material being mixed together, a cover of ceramic material covering the stirrer coils and adjacent parts on the side facing the furnace.

References Cited UNITED STATES PATENTS 2,513,082 6/1950 Dreyfus 1326 2,888,541 5/1959 Netzer 2l9l0.79 X 3,045,095 7/1962 Usher et al. 219-l0'.79 3,200,185 8/1965 Folgero et al. 1326 RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner. 

